Simplify the following expression: $k = \dfrac{a}{9} + \dfrac{a}{8}$
In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $9$ and $8$ $\lcm(9, 8) = 72$ $ k = \dfrac{8}{8} \cdot \dfrac{a}{9} + \dfrac{9}{9} \cdot \dfrac{a}{8} $ $k = \dfrac{8a}{72} + \dfrac{9a}{72}$ $k = \dfrac{8a +9a}{72}$ $k = \dfrac{17a}{72}$